Yahoo appears to be turning to patent licensing to boost its fortunes.

The foundering Web pioneer is threatening legal action against Facebook if the social-networking giant does not agree to license 10 to 20 patents held by Yahoo, according to The New York Times. The patents at issue relate to advertising, Web site personalization, social networking, and chat services, the newspaper reported, citing unidentified people briefed on the matter.

Yahoo didn't respond to a CNET request for comment but told the Times that, "We must insist that Facebook either enter into a licensing agreement or we will be compelled to move forward unilaterally to protect our rights."

Facebook said it had only just learned of matter and could not comment on the matter without further study.

"Yahoo contacted us at the same time they called the New York Times and so we haven't had the opportunity to fully evaluate their claims," a Facebook representative told CNET.